In the prior art, hydraulically driven fans have been proposed for cooling of internal combustion engines used in automotive vehicles. However, the proposed systems do not provide an optimal solution. Specifically, many of these systems provide several non-optimal characteristics, including (1) sporadic over-speeding of the fan, producing a situation called xe2x80x9cfan roar,xe2x80x9d and (2) waste of hydraulic energy, especially at low and high engine speeds.
One of the problems inherent to automotive hydraulic systems is compensating for the broad range of engine speeds across which the systems must function. At idle, while engine speed is perhaps 500-700 rpm, there is generally a shortage of flow thus forcing small working chambers and higher system pressure to complete the work. At high engine speeds, such as 3000-5000 rpm, there is an overabundance of flow causing unnecessary hydraulic system power draw and heat generation unless the system pump to working chamber displacement ratios are adjusted.
A means of resolving the issue is through the use of a variable displacement pump, which allows flow production to be adjusted throughout operating ranges.
An alternate solution, as described in U.S. Pat. No. 5,561,978, is to provide a plurality of displacement chambers in the hydraulic load or motor assembly. U.S. Pat. No. 5,561,978 describes means by which flow is introduced to a second motor chamber when the system pressure exceeds some specific predetermined point. The second chamber eventually contributes working force or torque to the load lowering the overall system pressure and allowing the high flow rates produced at high engine speeds to be used effectively.
In this type of system, any time the system pressure is below a predetermined setpoint, all work is done by the first working chamber or motor regardless of engine/pump speed and thus corresponding available flow. This will unnecessarily raise system pressure, power draw and in most cases hydraulic line noise. In a hydraulic load such as a hydraulic cooling fan there would be at least the following two such solutions. Given that the fan speed control allows incremental increases in speed according to cooling needs, the maximum available fan speed would seldom be deployed at idle conditions thus there would be a substantial amount of operating time in which flow to both working chambers would allow the necessary output shaft speeds to be obtained while maintaining system pressures at a substantially lower level. In the second general case, maximum fan speeds at idle would require that all available flow be channeled to a single working chamber to meet the output shaft speed needs. In this case, the engine speeds would increase, as in city traffic, more flow would allow at some point for the second working chamber to be utilized again lowering system pressure and saving power.
U.S. Pat. No. 6,021,641 describes an improvement of the art of U.S. Pat. Nos. 5,561,978 and 5,687,568 which reduces power consumption by employing a separate valve which senses the pressure across the main control valve to meter flow to the second load, in this case a hydraulic motor.
This mechanism is dependent on use of two separate high precision plunger, spring and bore assemblies. This second assembly is an obvious additional cost and also creates additional leakage path for high-pressure oil to the nonproductive grade motor, thereby reducing performance during a critical maximum idle speed operational point at which an idle motor only is producing torque to drive the fan. Further, the second plunger in U.S. Pat. No. 6,021,641 is controlled by the pressure differential across the main control valve after it has completely closed off the primary bypass path. After the primary bypass path is closed, the pressure differential across the primary plunger continues to decline with further pilot actuator stroke, however, this pressure decline is steep and in some cases erratic thus creating discontinuities in fan speed control. Minor changes in tolerance of any number of components can further influence the interaction between the two plungers yielding further negative effects on fan speed resolution.
The object of the present improvement of the art, as defined in the following description and claims, is to, among other things, modify the design to integrate the primary bypass valve and the secondary grade motor metering valve into an arrangement which requires only one moving valve which is much less susceptible to tolerances and/or subject to erratic movement resulting in poor fan speed control.
In another aspect, this invention comprises method of operating a cooling system in an automotive vehicle, comprising the following steps: operating two hydraulic motors coupled together to drive a cooling fan, selectively operating the motors under one of the following conditions: applying flow at pressure P1 to both motors, applying flow at pressure P2 to both motors, and applying substantially no flow to one motor, flow at pressure P3 to the other motor, wherein P3 is greater than P2, which is greater than P1.
In still another aspect, this invention comprises cooling system for a motor vehicle, comprising a fan, a control means for detecting a high engine speed, and placing a limit on fan speed for a time period.
In yet another aspect, this invention comprises a method of operating a cooling system for a motor vehicle, comprising the following steps running a fan, detecting onset of a high engine speed, and in response to the onset, placing a limit on fan speed for a time period.
In still another aspect, this invention comprises a method of controlling a hydraulically powered fan driven by a hydraulic pump in an automotive vehicle, the improvement comprising the following steps: controlling fan speed based control parameters which include engine speed, placing a limit on fan speed after an onset of a high engine speed, and removing the limit if the high engine speed persists for a predetermined period.
In yet another aspect, this invention comprises a hydraulically powered fan driven by a hydraulic pump in an automotive vehicle, the improvement comprising: means for controlling fan speed based control parameters which include engine speed, means for placing a limit on fan speed after an onset of a high engine speed, and means for removing the limit if the high engine speed persists for a predetermined period.
An object of the invention is to provide an improved hydraulic coolant fan for automotive vehicles.
A further object of the invention is to provide a hydraulic fan for an automotive vehicle, which reduces both wasted hydraulic energy and unnecessary fan roar.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.